Long before Europeans settled here, Pacific Coast tribes knew to avoid eating shellfish when the waves sparkled at night.
Their folk wisdom was sound science. The toxic algae responsible for paralytic shellfish poisoning light up seawater with bioluminescence when cells are agitated in the surf.
More recently, a stealthier type of algae has been blooming along the West Coast. They leave no telltale luminescence even though they can kill seabirds and marine mammals and make people sick.
Public health authorities did not become aware that the algae produce a neurotoxin, domoic acid, until 1987, when three people died and more than 100 fell ill in Canada after eating contaminated mussels. Some of the patients have required lifelong care because of memory loss and other complications.
Since then, Washington state health officials have repeatedly shut down the seasonal razor clam harvest when they detect domoic acid at levels above the safety threshold set by the U.S. Food and Drug Administration.
Such closures, disappointing many of the 30,000 people who regularly turn out for a harvest, are intended to prevent high-dose poisonings, which typically begin with abdominal cramps, vomiting and diarrhea, and can lead to seizures, memory loss, coma and death.
Now, scientists are trying to learn whether regular exposure to low levels of domoic acid can cause permanent harm.
Lynn Grattan, a neuroscientist at the University of Maryland School of Medicine, began searching for such effects after seeing a presentation on how domoic acid damages a memory center in the brains of California sea lions.
"I started asking, 'How long is it going to be before we see this happening in humans?' " she recalled.
Grattan looked for people who regularly ate shellfish in areas where domoic acid was a concern.
She started small — by testing about 70 members of the Quileute Tribe in La Push, Wash. She found that mental development in children born in 1998, a year marked by elevated domoic acid levels in shellfish, lagged that of infants born in other years.
Children who consumed shellfish during years with elevated levels of domoic acid had poorer memory performance than those who didn't eat shellfish.
The study's subject pool was too limited to provide definitive answers. So last year Grattan's team of researchers launched a five-year study of 625 coastal-dwelling Native Americans of all ages from five tribes to test for effects of repeated low-level exposures to domoic acid. The researchers say they will also examine whether the current FDA safety standard is adequate.
Edward D. Levin, a professor of psychiatry and behavioral sciences at Duke University, believes that looking at the effect on early child development is crucial.
In his own studies, he injected pregnant rats with low-level doses of domoic acid that did not affect the mothers, but that caused lifelong spatial memory problems in their offspring.
"The remarkable thing from our study is the persistence of effects after one single injection," Levin said. "You can imagine a pregnant woman who eats contaminated shellfish during a bloom. That one day can cause a problem for a lifetime for her kid."
These studies are part of an emerging field of research on the long-term effects of toxins in marine algae and bacteria on human health.
"We estimate there are 60,000 poisonings from marine biotoxins each year, even though they are vastly unreported," said Allen Dearry, an associate director of the National Institute of Environmental Health Sciences. "It's important we understand the long-term impact on public health."
The institute funded the researchers who last year tested the memory of Leilani Jones-Chubby, a member of the Quinault Indian Nation here on Washington's coast.
One part of the test required Jones-Chubby, a 55-year-old grandmother, to recall lists of names and numbers that had been read to her. She said she did poorly. "I have a real bad memory."
Jones-Chubby wonders if shellfish toxin led to the forgetfulness exhibited by her late mother, who was diagnosed with Alzheimer's disease.
But even if clams are causing memory loss, she doesn't know what the tribe could do about it.
Razor clams are a staple of the diet of the 3,000-member tribe. The Quinault language even has a word meaning "clam hungry."
"We live off the land," said Jones-Chubby, digging through her freezer to show plastic bags of frozen clams next to elk meat. She and her family eat clams two or three times a week, and she has dug clams to earn extra money since she was a girl trying to pay for school clothes.
"When I got a divorce, clam digging supported me and my family," she said. "Clam digging is not just our way of life, but a necessity of life."